The present invention relates to an apparatus and method for performing high-rate cathode sputtering utilizing a hollow cathode sputter source for depositing high purity thin film layers of desired physical, chemical, and/or mechanical properties. The invention has particular utility in the manufacture of magnetic or magneto-optical (xe2x80x9cMOxe2x80x9d) recording media comprising a layer stack or laminate of a plurality of layers on a suitable substrate, e.g., a disk-shaped substrate, wherein the layer stack or laminate includes an upper, carbon-based protective layer.
Magnetic and MO media are widely employed in various applications, particularly in the computer industry for data/information storage and retrieval purposes. A magnetic medium in e.g., disk form, such as utilized in computer-related applications, comprises a non-magnetic substrate, e.g., of glass, ceramic, glass-ceramic composite, polymer, metal, or metal alloy, typically an aluminum (Al)-based alloy such as aluminum-magnesium (Alxe2x80x94Mg), having at least one major surface on which a layer stack comprising a plurality of thin film layers constituting the medium are sequentially deposited. Such layers may include, in sequence from the workpiece (substrate) deposition surface, a plating layer, e.g., of amorphous nickel-phosphorus (Nixe2x80x94P), a polycrystalline underlayer, typically of chromium (Cr) or a Cr-based alloy such as chromium-vanadium (Crxe2x80x94V), a magnetic layer, e.g., of a cobalt (Co)-based alloy, and a protective overcoat layer, typically of a carbon-based material having good mechanical (i.e., tribological) properties. A similar situation exists with MO media, wherein a layer stack is formed which comprises a reflective layer, typically of a metal or metal alloy, one or more rare-earth thermo-magnetic (RE-TM) alloy layers, one or more dielectric layers, and a protective overcoat layer, for functioning as reflective, transparent, writing, writing assist, and read-out layers, etc.
According to conventional manufacturing methodology, a majority of the above-described layers constituting magnetic and/or MO recording media are deposited by cathode sputtering, typically by means of multi-cathode and/or multi-chamber sputtering apparatus wherein a separate cathode comprising a selected target material is provided for deposition of each component layer of the stack and the sputtering conditions are optimized for the particular component layer to be deposited. Each cathode comprising a selected target material can be positioned within a separate, independent process chamber, in a respective process chamber located within a larger chamber, or in one of a plurality of separate, interconnected process chambers each dedicated for deposition of a particular layer. According to such conventional manufacturing technology, media substrates, typically in disk form, are serially transported, in linear or circular fashion, depending upon the physical configuration of the particular apparatus utilized, from one sputtering target and/or process chamber to another for sputter deposition of a selected layer thereon. In some instances, again depending upon the particular apparatus utilized, sputter deposition of the selected layer commences only when the substrate (e.g., disk) deposition surface is positioned in complete opposition to the sputtering target, e.g., after the disk has fully entered the respective process chamber or area in its transit from a preceding process chamber or area, and is at rest. Stated somewhat differently, sputter deposition commences and continues for a predetermined interval only when the substrate is not in motion, i.e., deposition occurs onto static substrates. In other instances, however, substrate transport, hence motion, between adjoining process chambers or areas is continuous, and sputter deposition of each selected target material occurs in a xe2x80x9cpass-byxe2x80x9d mode onto moving substrates as the latter pass by each cathode/target assembly.
Regardless of which type of sputtering apparatus is employed for forming the thin layer stacks constituting the magnetic recording medium, it is essential for obtaining high recording density, high quality media that each of the component layers be deposited in a highly pure form and with desired physical, chemical, and/or mechanical properties. Film purity depends, inter alia, upon the purity of the atmosphere in which the film is grown; hence films are grown in as low a vacuum as is practicable. However, in order to maintain the rate of sputtering of the various target materials at levels consistent with the throughput requirements of cost-effective, large-scale media manufacture, the amount of sputtering gas in the process chamber(s), typically argon (Ar), must be maintained at levels which generate and sustain plasmas containing an adequate amount of ions for providing sufficient bombardment and sputtering of the respective target material. The requirement for maintaining an adequate amount of Ar sputtering gas for sustaining the plasma at an industrially viable level, however, is antithetical to the common practice of applying a negative voltage bias to the substrates during sputter deposition thereon for achieving optimum film properties, such as, for example, the formation of carbon-based protective films containing a greater proportion of desirable sp3 bonds (as in diamond), for use as protective overcoat layers in the manufacture of disk media. Contamination of the bias-sputtered films with Ar atoms occurs because the plasmas almost always contain a large number of Ar+ ions, relative to the number of ions of the sputtered target species, which Ar+ ions are accelerated towards the negatively biased substrate surfaces and implanted in the growing films along with the sputtered target species.
Accordingly, there exists a need for improved means and methodology for depositing, by sputtering techniques and at deposition rates consistent with the throughput requirements of automated manufacturing processing, thin films of high purity and of desired physical, chemical, and/or mechanical properties, which means and methodology overcomes the drawback associated with the apparent competing factors of the presence of a large number of ions of the sputtering gas (e.g., Ar) in the plasma and the usual application of a negative polarity substrate bias during film deposition, as described supra. More specifically, there exists a need for improved means and methodology for sputtering high purity, high quality, thin film layer stacks or laminates having optimal physical, chemical, and/or mechanical properties for use in the manufacture of single- and/or dual-sided magnetic and/or MO media, e.g., in the form of disks, which means and methodology provide rapid simple, and cost-effective formation of such media, as well as various other products and manufactures comprising at least one thin film layer.
The present invention addresses and solves compositional, throughput, and film property problems attendant upon the deposition of thin film layers by sputtering of target materials in plasmas comprising a sputter gas, which thin film deposition is utilized, inter alia, in the manufacture of high quality, thin film magnetic and/or MO recording media, while maintaining full compatibility with all aspects of conventional automated manufacturing technology therefor. Further, the means and methodology afforded by the present invention enjoy diverse utility in the manufacture of various devices and articles requiring high purity, high quality thin films with optimal physical, chemical, and/or mechanical properties.
An advantage of the present invention is an improved hollow cathode sputter source.
Another advantage of the present invention is an improved apparatus for sputter coating of a workpiece surface, comprising a hollow cathode sputter source.
Yet another advantage of the present invention is an improved method of coating over a workpiece, utilizing a hollow cathode sputter source.
Still another advantage of the present invention is an improved method of forming a carbon-containing protective coating on a substrate.
Additional advantages and other features of the present invention will be set forth in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from the practice of the present invention. The advantages of the present invention may be realized and obtained as particularly pointed out in the appended claims.
According to an aspect of the present invention, the foregoing and other advantages are obtained in part by a hollow cathode sputter source providing a sputtered particle flux having an increased ionization probability, comprising:
(a) a box-shaped chamber defining an interior space, the chamber being open at the top and comprising a flat, horizontal bottom wall and a first pair of opposing, flat, vertical sidewalls connected at the lateral ends thereof by a second pair of opposing, flat, vertical sidewalls, the bottom wall and each of the sidewalls comprising an electrically conductive material, and at least the interiorly facing surfaces of the bottom wall and each of the sidewalls adapted to comprise a sputtering target material; and
(b) a magnet means having a pair of vertically spaced-apart magnetic poles of opposite polarity, the magnet means continuously extending around the periphery of the box-shaped chamber along the exterior surface of each of the sidewalls for generating magnetic field lines which emerge from and re-enter each of the interiorly facing surfaces of the sidewalls at vertically spaced-apart locations, the magnet means adapted to generate an electron Hall drift current traveling in opposite directions along the interiorly facing surfaces of the first and second pairs of opposing sidewalls in a plasma discharge generated within the interior space during operation of the sputter source.
According to embodiments of the present invention, the first and second pairs of sidewalls are of equal lengths and the chamber is square-shaped or the first and second pairs of sidewalls are of unequal lengths and the chamber is rectangularly-shaped; and all of said sidewalls are electrically interconnected.
In particular embodiments according to the present invention, the bottom wall is electrically connected to the sidewalls, and the source further comprises:
(c) means for applying an electrical potential to the bottom wall and the sidewalls.
According to other embodiments of the present invention, the bottom wall is electrically isolated from the sidewalls, and the source further comprises:
(d) means for applying the same or different electrical potentials to the bottom wall and the sidewalls.
In accordance with embodiments of the present invention, the magnet means (b) comprises an electromagnet coil or a permanent magnet, and according to particular embodiments of the present invention, the permanent magnet comprises an assembly of a plurality of permanent magnets.
According to particular embodiments of the present invention, the electrically conductive material of the bottom wall and each of the sidewalls is the sputtering target material and is a metal or a carbon material, e.g., graphite.
In accordance with another aspect of the present invention, an improved apparatus for sputter coating a workpiece comprises the hollow cathode sputter source of the present invention and a workpiece mounting means for positioning a workpiece in spaced opposition to the open top of the box-shaped chamber for receiving sputtered target material from the hollow cathode sputter source.
According to particular embodiments of the present invention, the sputter coating apparatus further includes means for applying an electrical bias potential to the workpiece mounting means.
Yet another aspect of the present invention is an improved method of sputter coating a workpiece, comprising the steps of:
(a) providing a hollow cathode sputter source for generating a sputtered particle flux having an increased ionization probability, comprising:
(i) a box-shaped chamber defining an interior space, the chamber being open at the top and comprising a flat, horizontal bottom wall and a first pair of opposing, flat, vertical sidewalls connected at the lateral ends thereof by a second pair of opposing, flat, vertical sidewalls, the bottom wall and each of the sidewalls comprising an electrically conductive material, and at least the interiorly facing surfaces of the bottom wall and each of the sidewalls comprising a sputtering target material; and
(ii) a magnet means having a pair of vertically spaced-apart magnetic poles of opposite polarity, the magnet means continuously extending around the periphery of the box-shaped chamber along the exterior surface of each of the sidewalls for generating magnetic field lines which emerge from and re-enter each of the interiorly facing surfaces of the sidewalls at vertically spaced-apart locations;
(b) positioning a workpiece having a deposition surface in spaced opposition to the open top of the box-shaped chamber for receiving sputtered target material from the hollow cathode sputter source;
(c) supplying a sputter gas to the interior space of the box-shaped chamber;
(d) applying an electrical potential to the hollow cathode sputter source to generate a plasma discharge therein for sputtering the target material from said interiorly facing surfaces of the bottom wall and each of the sidewalls, the plasma discharge being characterized by an electron Hall drift current traveling in opposite directions along the interiorly facing surfaces of the first and second pairs of opposing sidewalls; and
(e) forming a layer of sputtered target material over the surface of the workpiece.
According to embodiments of the present invention, step (a)(i) comprises providing a box-shaped chamber wherein all of the sidewalls are electrically interconnected, and step (d) comprises applying the electrical potential to the sidewalls.
In accordance with particular embodiments of the present invention, step (a)(i) further comprises providing a box-shaped chamber wherein the bottom wall is electrically connected to the sidewalls, and step (d) comprises applying the electrical potential to the sidewalls and the bottom wall; whereas, according to other embodiments of the present invention, step (a)(i) further comprises providing a box-shaped chamber wherein the bottom wall is electrically isolated from the sidewalls, and step (d) comprises applying the same or different electrical potentials to the bottom wall and the sidewalls.
According to further embodiments of the present invention, the electrically conductive material of the bottom wall and each of said sidewalls is the sputtering target material, e.g., a metal material or a carbon material, such as graphite.
In accordance with embodiments of the present invention, step (b) further comprises applying an electrical bias potential to the workpiece for accelerating ions of the sputtered target material towards the workpiece surface for deposition thereon; the sputtering target material is a metal material or a carbon material; and the workpiece is a disk-shaped substrate for a magnetic or magneto-optical (MO) recording medium and step (e) comprises forming a carbon-containing protective layer over the surface of the medium.
Still another aspect of the present invention is a sputter source, comprising:
a box-shaped hollow cathode sputtering target defining an interior space and comprising a bottom and first and second pairs of electrically interconnected, opposing vertical sidewalls; and
means for generating an electron Hall drift current traveling in opposite directions along interiorly facing surfaces of the first and second pairs of opposing sidewalls.
Additional advantages and aspects of the present invention will become readily apparent to those skilled in the art from the following detailed description, wherein embodiments of the present invention are shown and described, simply by way of illustration of the best mode contemplated for practicing the present invention. As will be described, the present invention is capable of other and different embodiments, and its several details are susceptible of modification in various obvious respects, all without departing from the spirit of the present invention. Accordingly, the drawings and description are to be regarded as illustrative in nature, and not as limitative.